I mean, if anything your list proves my point. They're not used at all. Also, I was asking parent for his implementation - I'm assuming he hasn't written any actual code though.
This is not a valid argument, invalidating discussion of merit of thing based on not having personally created incarnation of said thing would remove 99% of debate of FOSS to no ones benefit.
My only problem with Jack is that Firefox (and Chrome too, afaik) absolutely insists on using Pulse, so you have to make both play nice if you want to use Youtube while working on music (which is actually pretty common). This can be a bit of a pain (funny things happen after suspend/resume). Still it's so useful for music/sound production, I put up with it :-)
Jack does not overlap with PulseAudio. Pipewire does, but it came later and has the explicit purpose of unifying Jack and PulseAudio.
Upstart is decidedly inferior to systemd; the event-based architecture is much harder to understand and apply than the target/dependency architecture of systemd. And systemd is in use in distros ranging from embedded (LibreELEC) to enterprise server, it must be doing _something_ right...
Regarding the event driven architecture: it is far easier to understand than systemd's dependency system. But it is indeed more difficult to apply, particularly because it is a departure from how most systems work currently and in the sysvinit past.
I enjoy the architecture, and hope to continue developing Upstart/startup or at least work with a similar model.
And yet none of those init systems are really being used in any significant way. It doesn't detract from them, but then they don't detract from systemd.
dmix, jack, pipewire
* now maintained at https://gitlab.com/chinstrap/startup